The general shape of the tank or receptacle follows that of the older metal tanks used on machines of this kind. Hempel U.S. Pat. No. 2,845,266 illustrates such a metal tank. It is designed to fit on the front wall of a tape dispensing machine to contain water, to fit onto a heating element to heat the water, and to support a brush to transmit the heated water by capillarity to the top of the tank, where, as the tape passes across the brush, the under gummed surface of the tape is moistened for application to an object such as a carton.
A problem with the tanks, of metal, usually zinc, is that they have a serious corrosion problem. This is thought to be increased by the fact that they are subjected to localized heating and contain water as an electrolyte.
An additional problem with the metal tank is that it is relatively difficult to clean, in that deposits from the water adhere tightly to its surfaces. The plastic tank is easier to clean, as the deposits can easily be removed from its surfaces.
A further problem with this type of tank is that the metal conducts heat well, and, being in close association with the heating element, causes the whole receptacle to become hot to the touch and capable of burning a user who touches it inadvertently.
Prior efforts to make plastic receptacles have failed, although plastic, being a relatively poor conductor of heat, does not afford the burning hazard of metal receptacles, and is also not subject to the corrosion problems of the metal tanks. It is necessary for efficiency of the heater to have a good heat conduction from the heating element that projects from the front wall of the tape machine into the water within the receptacle. It is also necessary to have the receptacle watertight so that it will not leak the water. Prior efforts with plastic receptacles have failed to combine good heat conduction and good strength, with absence of leaking.